Field of the Invention
This invention relates to biofabricated leather materials composed of unbundled and randomly-oriented trimeric collagen fibrils that exhibit superior strength, non-anisotropic properties, and uniformity by comparison to conventional leather products, but which have the look, feel and other aesthetic properties of natural leather. Unlike synthetic leather products composed of plastic resins, the biofabricated leather of the invention is based on collagen, a natural component of leather.
Description of Related Art
Leather. Leather is used in a vast variety of applications, including furniture upholstery, clothing, shoes, luggage, handbag and accessories, and automotive applications. The estimated global trade value in leather is approximately US $100 billion per year (Future Trends in the World Leather Products Industry and Trade, United Nations Industrial Development Organization, Vienna, 2010) and there is a continuing and increasing demand for leather products. New ways to meet this demand are required in view of the economic, environmental and social costs of producing leather. To keep up with technological and aesthetic trends, producers and users of leather products seek new materials exhibiting superior strength, uniformity, processability and fashionable and appealing aesthetic properties that incorporate natural components.
Natural leathers are produced from the skins of animals which require raising livestock. However, the raising of livestock requires enormous amounts of feed, pastureland, water, and fossil fuels. It also produces air and waterway pollution, including production of greenhouse gases like methane. Some states in the United States, such as California, may impose taxes on the amounts of pollutants such as methane produced by livestock. As the costs of raising livestock rise, the cost of leather will rise.
The global leather industry slaughters more than a billion animals per year. Most leather is produced in countries that engage in factory farming, lack animal welfare laws, or in which such laws go largely or completely unenforced. This slaughter under inhumane conditions is objectionable to many socially conscious people. Consequently, there is a demand from consumers with ethical, moral or religious objections to the use of natural leather products for products humanely produced without the mistreatment or slaughter of animals or produced in ways that minimize the number of animals slaughtered.
The handling and processing of animal skins into leather also poses health risks because the handling animal skins can expose workers to anthrax and other pathogens and allergens such as those in leather dust. Factory farming of animals contributes to the spread of influenza (e.g. “bird flu”) and other infectious diseases that may eventually mutate and infect humans. Animal derived products are also susceptible to contamination with viruses and prions (“mad cow disease”). For producer and consumer peace of mind, there exists a demand for leather products that do not present these risks.
Natural leather is generally a durable and flexible material created by processing rawhide and skin of an animal, such as cattle hides. This processing typically involves three main parts: preparatory stages, tanning, and retanning. Leather may also be surface coated or embossed.
Numerous ways are known to prepare a skin or hide and convert it to leather. These include salting or refrigerating a hide or skin to preserve it; soaking or rehydrating the hide in an aqueous solution that contains surfactants or other chemicals to remove salt, dirt, debris, blood, and excess fat; defleshing or removing subcutaneous material from the hide; dehairing or unhairing the hide remove most of the hair; liming the hide to loosen fibers and open up collagen bundles allowing it to absorb chemicals; splitting the hide into two or more layers; deliming the hide to remove alkali and lower its pH; bating the hide to complete the deliming process and smooth the grain; degreasing to remove excess fats; frizzing; bleaching; pickling by altering the pH; or depickling,
Once the preparatory stages are complete, the leather is tanned. Leather is tanned to increase its durability compared to untreated hide. Tanning converts proteins in the hide or skin into a stable material that will not putrefy while allowing the leather material to remain flexible. During tanning, the skin structure may be stabilized in an “open” form by reacting some of the collagen with complex ions of chromium or other tanning agents. Depending on the compounds used, the color and texture of the leather may change.
Tanning is generally understood to be the process of treating the skins of animals to produce leather. Tanning may be performed in any number of well-understood ways, including by contacting a skin or hide with a vegetable tanning agent, chromium compound, aldehyde, syntan, synthetic, semisynthetic or natural resin or polymer, or/and tanning natural oil or modified oil. Vegetable tannins include pyrogallol- or pyrocatechin-based tannins, such as valonea, mimosa, ten, tara, oak, pinewood, sumach, quebracho and chestnut tannins; chromium tanning agents include chromium salts like chromium sulfate; aldehyde tanning agents include glutaraldehyde and oxazolidine compounds, syntans include aromatic polymers, polyacrylates, polymethacrylates, copolymers of maleic anhydride and styrene, condensation products of formaldehyde with melamine or dicyandiamide, lignins and natural flours.
Chromium is the most commonly used tanning material. The pH of the skin/hide may be adjusted (e.g., lowered, e.g. to pH 2.8-3.2) to allow penetration of the tanning agent; following penetration the pH may be raised to fix the tanning agent (“basification” to a slightly higher level, e.g., pH 3.8-4.2 for chrome).
After tanning, a leather may be retanned. Retanning refers to the post-tanning treatment that can include coloring (dying), thinning, drying or hydrating, and the like. Examples of retanning techniques include: tanning, wetting (rehydrating), sammying (drying), neutralization (adjusting pH to a less acidic or alkaline state), dyeing, fat liquoring, fixation of unbound chemicals, setting, conditioning, softening, buffing, etc.
A tanned leather product may be mechanically or chemically finished. Mechanical finishing can polish the leather to yield a shiny surface, iron and plate a leather to have a flat, smooth surface, emboss a leather to provide a three dimensional print or pattern, or tumble a leather to provide a more evident grain and smooth surface. Chemical finishing may involve the application of a film, a natural or synthetic coating, or other leather treatment. These may be applied, for example, by spraying, curtain-coating or roller coating.
In animal hide, variations in fibrous collagen organization are observed in animals of different ages or species. These differences affect the physical properties of hides and differences in leather produced from the hides. Variations in collagen organization also occur through the thickness of the hide. The top grain side of hide is composed of a fine network of collagen fibrils while deeper sections (corium) are composed of larger fiber bundles (FIG. 2). The smaller fibril organization of the grain layer gives rise to a soft and smooth leather aesthetic while the larger fiber bundle organization of deeper regions gives rise to a rough and course leather aesthetic. The porous, fibrous organization of collagen in a hide allows applied molecules to penetrate, stabilize, and lubricate it during leather tanning. The combination of the innate collagen organization in hide and the modifications achieved through tanning give rise to the desirable strength, drape and aesthetic properties of leather.
The top grain surface of leather is often regarded as the most desirable due to its smoothness and soft texture. This leather grain contains a highly porous network of organized collagen fibrils. Endogenous collagen fibrils are organized to have lacunar regions and overlapping regions; see the hierarchical organization of collagen depicted by FIG. 1. The strengths, microscale porosity, and density of fibrils in a top grain leather allow tanning or fatliquoring agents to penetrate it, thus stabilizing and lubricating the collagen fibrils, producing a soft, smooth and strong leather that people desire.
Leather hides can be split to obtain leather that is mostly top grain. The split hide can be further abraded to reduce the coarser grained corium on the split side, but there is always some residual corium and associated rough appearance. In order to produce leather with smooth grain on both sides, it is necessary to combine two pieces of grain, corium side facing corium side and either sew them together or laminate them with adhesives with the smooth top grain sides facing outward. There is a demand for a leather product that has a smooth, top grain-like surface on both its sides, because this would avoid the need for splitting, and sewing or laminating two split leather pieces together.
Control of the final properties of leather is limited by the natural variation in collagen structure between different animal hides. For example, the relative thickness of grain to corium in goat hide is significantly higher than that in kangaroo hide. In addition, the weave angle of collagen fiber bundles in kangaroo corium are much more parallel to the surface of the hide, while fiber bundles in bovine corium are oriented in both parallel and perpendicular orientations to the surface of the hide. Further, the density of fiber bundles varies within each hide depending on their anatomical location. Hide taken from butt, belly, shoulder, and neck can have different compositions and properties. The age of an animal also affects the composition of its hide, for example, juvenile bovine hide contains smaller diameter fibers than the larger fiber bundles found in adult bovine hide.
The final properties of leather can be controlled to some extent through the incorporation of stabilizing and lubricating molecules into the hide or skin during tanning and retanning, however, the selection of these molecules is limited by the need to penetrate the dense structure of the skin or hide. Particles as large as several microns in diameter have been incorporated into leather for enhanced lubrication; however, application of these particles is limited to hides with the largest pore sizes. uniformly distributing the particles throughout the hide presents many challenges.
Due to the size limitations of materials that can uniformly penetrate the hide, leather composite materials are often laminates of leather and thin layers of other materials such as Kevlar or nylon for mechanical reinforcement, or polyurethanes and acrylics for aesthetically desirable surfaces. Construction of leather with a dispersed secondary material phase has not been achieved.
To address this limitation of natural leather, the inventors describe the fabrication of leather composites in which a continuous phase of collagen fibrils can encapsulate dispersed fibers and three dimensional materials. This technology enables the fabrication of a new class of leather materials with enhanced functionality.
While fibrillation of soluble collagens and collagen-like proteins has been widely explored to produce collagen hydrogels for biomedical applications, harnessing this phenomena to fabricate leather-like composite materials has never been reported. By starting with an aqueous mixture of collagen monomers or fibrils, virtually any material can be readily added to the mixture and further encapsulated into biofabricated leather. Further, the combination of a continuous collagen fibril phase with encapsulated fiber phase, composite materials with a grain-like aesthetic and a range of enhanced mechanical properties can be achieved.
Many leather applications require a durable product that doesn't rip or tear, even when the leather has been stitched together. Typical products that include stitched leather and require durable leather include automobile steering wheel covers, automobile seats, furniture, sporting goods, sport shoes, sneakers, watch straps and the like. There is a need to increase the durability of biofabricated leather to improve performance in these products.
The top grain surface of leather is often regarded as the most desirable due to its soft texture and smooth surface. As discussed previously, the grain is a highly porous network of collagen fibrils. The strength of the collagen fibril, microscale porosity, and density of fibrils in the grain allow tanning agent penetration to stabilize and lubricate the fibrils, producing a soft, smooth and stable material that people desire. While the aesthetic of the grain is very desirable, the strength and tear resistance of the grain is often a limitation for practical application of the grain alone. Therefore, the grain is often backed with corium, its naturally reinforcing collagen layer, or can be backed artificially with laminar layers of synthetic materials. The reinforced collagen composites described herein allow for a thick and uniform grain-like material with tunable mechanical properties through control of the continuous and dispersed phases.
In addition to enhanced mechanical properties, this bottom-up fabrication approach can also enable the encapsulation of materials for aesthetic functionality. For example, photoluminescent materials can be encapsulated into biofabricated leather. In traditional tanning, smaller nanoparticles to single molecules such as dyes are used to produce uniform coloration and aesthetic in leather. Since incorporation of dyes and aesthetic features relies on penetration of these molecules into the hide or skin, patterned features with controlled spatial organizations have not been possible with leather. Patterned photoluminescence features would provide unique functionality to leather including brand logos, personalization, aesthetically pleasing patterns, and anti-counterfeit technology.
The materials described herein can be used to produce biofabricated leathers with patterned photoluminescence features. Methods for forming a network of collagen fibrils in the presence or around a patterned substrate allows the encapsulation of precisely controlled patterns with larger dimensions within the biofabricated leather structure. Virtually any photoluminescent material can be incorporated or encapsulated in a biofabricated leather. In order to visualize the pattern, the light emitted from the embedded photoluminescent molecule must penetrate through the thickness of the leather. Recent studies have shown that light penetration into collagen rich materials such as skin is highly wavelength dependent and decreases exponentially through the thickness of the material. Therefore, variables such as the emission wavelength of the embedded photoluminescent material and the distance of the photoluminescent material from the surface of the biofabricated leather need to be considered to produce photoluminescent features that are visible by eye. Likewise, the intensity of the embedded photoluminescent material needs to be considered for features that are detectable by readers other than the eye, such as light emitting scanners for example. Further, three dimensional objects can be encapsulated into the biofabricated leather in order to produce unique surface textures and patterns. Surface patterns of traditional leather materials are limited by natural variations in the skin surface of the animal, or by the ability to emboss patterns onto the grain surface of leather. In order to achieve unique patterns with deep surface features, three dimensional objects can be embedded into biofabricated leather. These textures and patterns provide unique aesthetic features and can be used as logos for brand recognition.
Collagen.
Collagen is a component of leather. Skin, or animal hide, contains significant amounts of collagen, a fibrous protein. Collagen is a generic term for a family of at least 28 distinct collagen types; animal skin is typically type I collagen, although other types of collagen can be used in forming leather including type III collagen. Collagens are characterized by a repeating triplet of amino acids, -(Gly-X-Y)n- and approximately one-third of the amino acid residues in collagen are glycine. X is often proline and Y is often hydroxyproline, though there may be up to 400 possible Gly-X-Y triplets. Different animals may produce different amino acid compositions of the collagen, which may result in different properties and in differences in the resulting leather.
The structure of collagen can consist of three intertwined peptide chains of differing lengths. Collagen triple helices (or monomers) may be produced from alpha-chains of about 1,050 amino acids long, so that the triple helix takes the form of a rod of about approximately 300 nm long, with a diameter of approximately 1.5 nm. In the production of extracellular matrix by fibroblast skin cells, triple helix monomers may be synthesized and the monomers may self-assemble into a fibrous form. These triple helices are held together by electrostatic interactions including salt bridging, hydrogen bonding, Van der Waals interactions, dipole-dipole forces, polarization forces, hydrophobic interactions, and/or covalent bonding. Triple helices can be bound together in bundles called fibrils, and fibrils can further assemble to create fibers and fiber bundles (FIG. 1). Fibrils have a characteristic banded appearance due to the staggered overlap of collagen monomers. The distance between bands is approximately 67 nm for Type I collagen. Fibrils and fibers typically branch and interact with each other throughout a layer of skin. Variations of the organization or crosslinking of fibrils and fibers may provide strength to the material. Fibers may have a range of diameters depending on the type of animal hide. In addition to type I collagen, skin (hides) may include other types of collagen as well, including type III collagen (reticulin), type IV collagen, and type VII collagen.
Various types of collagen exist throughout the mammalian body. For example, besides being the main component of skin and animal hide, Type I collagen also exists in cartilage, tendon, vascular ligature, organs, muscle, and the organic portion of bone. Successful efforts have been made to isolate collagen from various regions of the mammalian body in addition to the animal skin or hide. Decades ago, researchers found that at neutral pH, acid-solubilized collagen self-assembled into fibrils composed of the same cross-striated patterns observed in native tissue; Schmitt F. O. J. Cell. Comp Physiol. 1942; 20:11). This led to use of collagen in tissue engineering and a variety of biomedical applications. In more recent years, collagen has been harvested from bacteria and yeast using recombinant techniques.
Regardless of the type of collagen, all are formed and stabilized through a combination of physical and chemical interactions including electrostatic interactions including salt bridging, hydrogen bonding, Van der Waals interactions, dipole-dipole forces, polarization forces, hydrophobic interactions, and covalent bonding often catalyzed by enzymatic reactions. For Type I collagen fibrils, fibers, and fiber bundles, its complex assembly is achieved in vivo during development and is critical in providing mechanical support to the tissue while allowing for cellular motility and nutrient transport. Various distinct collagen types have been identified in vertebrates. These include bovine, ovine, porcine, chicken, and human collagens.
Generally, the collagen types are numbered by Roman numerals, and the chains found in each collagen type are identified by Arabic numerals. Detailed descriptions of structure and biological functions of the various different types of naturally occurring collagens are available in the art; see, e.g., Ayad et al. (1998) The Extracellular Matrix Facts Book, Academic Press, San Diego, Calif.; Burgeson, R E., and Nimmi (1992) “Collagen types: Molecular Structure and Tissue Distribution” in Clin. Orthop. 282:250-272; Kielty, C. M. et al. (1993) “The Collagen Family: Structure, Assembly And Organization In The Extracellular Matrix,” Connective Tissue And Its Heritable Disorders, Molecular Genetics, And Medical Aspects, Royce, P. M. and B. Steinmann eds., Wiley-Liss, NY, pp. 103-147; and Prockop, D. J- and K. I. Kivirikko (1995) “Collagens: Molecular Biology, Diseases, and Potentials for Therapy,” Annu. Rev. Biochem., 64:403-434.)
Type I collagen is the major fibrillar collagen of bone and skin comprising approximately 80-90% of an organism's total collagen. Type I collagen is the major structural macromolecule present in the extracellular matrix of multicellular organisms and comprises approximately 20% of total protein mass. Type I collagen is a heterotrimeric molecule comprising two α1(I) chains and one α2(I) chain, encoded by the COL1A1 and COL1A2 genes, respectively. Other collagen types are less abundant than type I collagen, and exhibit different distribution patterns. For example, type II collagen is the predominant collagen in cartilage and vitreous humor, while type III collagen is found at high levels in blood vessels and to a lesser extent in skin.
Type II collagen is a homotrimeric collagen comprising three identical al(II) chains encoded by the COL2A1 gene. Purified type II collagen may be prepared from tissues by, methods known in the art, for example, by procedures described in Miller and Rhodes (1982) Methods In Enzymology 82:33-64.
Type III collagen is a major fibrillar collagen found in skin and vascular tissues. Type III collagen is a homotrimeric collagen comprising three identical α1(III) chains encoded by the COL3A1 gene. Methods for purifying type III collagen from tissues can be found in, for example, Byers et al. (1974) Biochemistry 13:5243-5248; and Miller and Rhodes, supra.
Type IV collagen is found in basement membranes in the form of sheets rather than fibrils. Most commonly, type IV collagen contains two α1(IV) chains and one α2(IV) chain. The particular chains comprising type IV collagen are tissue-specific. Type IV collagen may be purified using, for example, the procedures described in Furuto and Miller (1987) Methods in Enzymology, 144:41-61, Academic Press.
Type V collagen is a fibrillar collagen found in, primarily, bones, tendon, cornea, skin, and blood vessels. Type V collagen exists in both homotrimeric and heterotrimeric forms. One form of type V collagen is a heterotrimer of two α1(V) chains and one α2(V) chain. Another form of type V collagen is a heterotrimer of α1(V), α2(V), and α3(V) chains. A further form of type V collagen is a homotrimer of α1(V). Methods for isolating type V collagen from natural sources can be found, for example, in Elstow and Weiss (1983) Collagen Rel. Res. 3:181-193, and Abedin et al. (1982) Biosci. Rep. 2:493-502.
Type VI collagen has a small triple helical region and two large non-collagenous remainder portions. Type VI collagen is a heterotrimer comprising α1(VI), α2(VI), and α3(VI) chains. Type VI collagen is found in many connective tissues. Descriptions of how to purify type VI collagen from natural sources can be found, for example, in Wu et al. (1987) Biochem. J. 248:373-381, and Kielty et al. (1991) J. Cell Sci. 99:797-807.
Type VII collagen is a fibrillar collagen found in particular epithelial tissues. Type VII collagen is a homotrimeric molecule of three al(VII) chains. Descriptions of how to purify type VII collagen from tissue can be found in, for example, Lunstrum et al. (1986) J. Biol. Chem. 261:9042-9048, and Bentz et al. (1983) Proc. Natl. Acad. Sci. USA 80:3168-3172.Type VIII collagen can be found in Descemet's membrane in the cornea. Type VIII collagen is a heterotrimer comprising two α1(VIII) chains and one α2(VIII) chain, although other chain compositions have been reported. Methods for the purification of type VIII collagen from nature can be found, for example, in Benya and Padilla (1986) J. Biol. Chem. 261:4160-4169, and Kapoor et al. (1986) Biochemistry 25:3930-3937.
Type IX collagen is a fibril-associated collagen found in cartilage and vitreous humor. Type IX collagen is a heterotrimeric molecule comprising α1(IX), α2(IX), and α3 (IX) chains. Type IX collagen has been classified as a FACIT (Fibril Associated Collagens with Interrupted Triple Helices) collagen, possessing several triple helical domains separated by non-triple helical domains. Procedures for purifying type IX collagen can be found, for example, in Duance, et al. (1984) Biochem. J. 221:885-889; Ayad et al. (1989) Biochem. J. 262:753-761; and Grant et al. (1988) The Control of Tissue Damage, Glauert, A. M., ed., Elsevier Science Publishers, Amsterdam, pp. 3-28.
Type X collagen is a homotrimeric compound of al(X) chains. Type X collagen has been isolated from, for example, hypertrophic cartilage found in growth plates; See, e.g., Apte et al. (1992) Eur J Biochem 206 (1):217-24.
Type XI collagen can be found in cartilaginous tissues associated with type II and type IX collagens, and in other locations in the body. Type XI collagen is a heterotrimeric molecule comprising α1(XI), α2(XI), and α3(XI) chains. Methods for purifying type XI collagen can be found, for example, in Grant et al., supra.
Type XII collagen is a FACIT collagen found primarily in association with type I collagen. Type XII collagen is a homotrimeric molecule comprising three α1(XII) chains. Methods for purifying type XII collagen and variants thereof can be found, for example, in Dublet et al. (1989) J. Biol. Chem. 264:13150-13156; Lunstrum et al. (1992) J. Biol. Chem. 267:20087-20092; and Watt et al. (1992) J. Biol. Chem. 267:20093-20099.
Type XIII is a non-fibrillar collagen found, for example, in skin, intestine, bone, cartilage, and striated muscle. A detailed description of type XIII collagen may be found, for example, in Juvonen et al. (1992) J. Biol. Chem. 267: 24700-24707.
Type XIV is a FACIT collagen characterized as a homotrimeric molecule comprising al(XIV) chains. Methods for isolating type XIV collagen can be found, for example, in Aubert-Foucher et al. (1992) J. Biol. Chem. 267:15759-15764, and Watt et al., supra.
Type XV collagen is homologous in structure to type XVIII collagen. Information about the structure and isolation of natural type XV collagen can be found, for example, in Myers et al. (1992) Proc. Natl. Acad. Sci. USA 89:10144-10148; Huebner et al. (1992) Genomics 14:220-224; Kivirikko et al. (1994) J. Biol. Chem. 269:4773-4779; and Muragaki, J. (1994) Biol. Chem. 264:4042-4046.
Type XVI collagen is a fibril-associated collagen, found, for example, in skin, lung fibroblast, and keratinocytes. Information on the structure of type XVI collagen and the gene encoding type XVI collagen can be found, for example, in Pan et al. (1992) Proc. Natl. Acad. Sci. USA 89:6565-6569; and Yamaguchi et al. (1992) J. Biochem. 112:856-863.
Type XVII collagen is a hemidesmosal transmembrane collagen, also known at the bullous pemphigoid antigen. Information on the structure of type XVII collagen and the gene encoding type XVII collagen can be found, for example, in Li et al. (1993) J. Biol. Chem. 268(12):8825-8834; and McGrath et al. (1995) Nat. Genet. 11(1):83-86.
Type XVIII collagen is similar in structure to type XV collagen and can be isolated from the liver. Descriptions of the structures and isolation of type XVIII collagen from natural sources can be found, for example, in Rehn and Pihlajaniemi (1994) Proc. Natl. Acad. Sci USA 91:4234-4238; Oh et al. (1994) Proc. Natl. Acad. Sci USA 91:4229-4233; Rehn et al. (1994) J. Biol. Chem. 269:13924-13935; and Oh et al. (1994) Genomics 19:494-499.
Type XIX collagen is believed to be another member of the FACIT collagen family, and has been found in mRNA isolated from rhabdomyosarcoma cells. Descriptions of the structures and isolation of type XIX collagen can be found, for example, in Inoguchi et al. (1995) J. Biochem. 117:137-146; Yoshioka et al. (1992) Genomics 13:884-886; and Myers et al., J. Biol. Chem. 289:18549-18557 (1994).
Type XX collagen is a newly found member of the FACIT collagenous family, and has been identified in chick cornea. (See, e.g., Gordon et al. (1999) FASEB Journal 13:A1119; and Gordon et al. (1998), IOVS 39:S1128.)
Any type of collagen, truncated collagen, unmodified or post-translationally modified, or amino acid sequence-modified collagen that can be fibrillated and crosslinked by the methods described herein can be used to produce a biofabricated material or biofabricated leather. Biofabricated leather may contain a substantially homogenous collagen, such as only Type I or Type III collagen or may contain mixtures of 2, 3, 4 or more different kinds of collagens.
Recombinant Collagen.
Recombinant expression of collagen and collagen-like proteins is known and is incorporated by reference to Bell, EP 1232182B1, Bovine collagen and method for producing recombinant gelatin; Olsen, et al., U.S. Pat. No. 6,428,978, Methods for the production of gelatin and full-length triple helical collagen in recombinant cells; VanHeerde, et al., U.S. Pat. No. 8,188,230, Method for recombinant microorganism expression and isolation of collagen-like polypeptides. Such recombinant collagens have not been used to produce leather.
Prokaryotic expression. In prokaryotic systems, such as bacterial systems, a number of expression vectors may be advantageously selected depending upon the use intended for the expressed polypeptide. For example, when large quantities of the animal collagens and gelatins of the invention are to be produced, such as for the generation of antibodies, vectors which direct the expression of high levels of fusion protein products that are readily purified may be desirable. Such vectors include, but are not limited to, the E. coli expression vector pUR278 (Ruther et al. (1983) EMBO J. 2:1791), in which the coding sequence may be ligated into the vector in frame with the lac Z coding region so that a hybrid AS-lacZ protein is produced; pIN vectors (Inouye et al. (1985) Nucleic Acids Res. 13:3101-3109 and Van Heeke et al. (1989) J. Biol. Chem. 264:5503-5509); and the like. pGEX vectors may also be used to express foreign polypeptides as fusion proteins with glutathione S-transferase (GST). In general, such fusion proteins are soluble and can easily be purified from lysed cells by adsorption to glutathione-agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned polypeptide of interest can be released from the GST moiety. A recombinant collagen may comprise collagen molecules that have not been post-translationally modified, e.g., not glycosylated or hydroxylated, or may comprise one or more post-translational modifications, for example, modifications that facilitate fibrillation and formation of unbundled and randomly oriented fibrils of collagen molecules. A recombinant collagen molecule can comprise a fragment of the amino acid sequence of a native collagen molecule that can form trimeric collagen fibrils or a modified collagen molecule or truncated collagen molecule having an amino acid sequence at least 70, 80, 90, 95, 96, 97, 98, or 99% identical or similar to a native collagen amino acid sequence (or to a fibril forming region thereof or to a segment substantially comprising [Gly-X-Y]n), such as those of bovine collagen, described by SEQ ID NOS: 1, 2 or 3 and by amino acid sequences of Col1A1, Col1A2, and Col1A3, described by Accession Nos. NP_001029211.1 (https://_www.ncbi.nlm.nih.gov/protein/77404252, last accessed Feb. 9, 2017), NP_776945.1 (https://_www.ncbi.nlm.nih.gov/protein/27806257 last accessed Feb. 9, 2017) and NP_001070299.1 (https://_www.ncbi.nlm.nih.gov/protein/116003881 last accessed Feb. 9, 2017) which are incorporated by reference. (These links have been inactivated by inclusion of an underline after the double slash.)
Such recombinant or modified collagen molecules will generally comprise the repeated -(Gly-X-Y)n-sequence described herein.
BLASTN may be used to identify a polynucleotide sequence having at least 70%, 75%, 80%, 85%, 87.5%, 90%, 92.5%, 95%, 97.5%, 98%, or 99% sequence identity to a reference polynucleotide such as a polynucleotide encoding a collagen polypeptide or encoding the amino acid sequences of SEQ ID NOS: 1, 2 or 3. A representative BLASTN setting optimized to find highly similar sequences uses an Expect Threshold of 10 and a Wordsize of 28, max matches in query range of 0, match/mismatch scores of 1/-2, and linear gap cost. Low complexity regions may be filtered or masked. Default settings of a Standard Nucleotide BLAST are described by and incorporated by reference to https://blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastn&PAGE_TYPE=BlastSearch&LINK _LOC=blasthome (last accessed Jan. 27, 2017).
BLASTP can be used to identify an amino acid sequence having at least 70%, 75%, 80%, 85%, 87.5%, 90%, 92.5%, 95%, 97.5%, 98%, or 99% sequence identity, or similarity to a reference amino acid, such as a collagen amino acid sequence, using a similarity matrix such as BLOSUM45, BLOSUM62 or BLOSUM80 where BLOSUM45 can be used for closely related sequences, BLOSUM62 for midrange sequences, and BLOSUM80 for more distantly related sequences. Unless otherwise indicated a similarity score will be based on use of BLOSUM62. When BLASTP is used, the percent similarity is based on the BLASTP positives score and the percent sequence identity is based on the BLASTP identities score. BLASTP “Identities” shows the number and fraction of total residues in the high scoring sequence pairs which are identical; and BLASTP “Positives” shows the number and fraction of residues for which the alignment scores have positive values and which are similar to each other. Amino acid sequences having these degrees of identity or similarity or any intermediate degree of identity or similarity to the amino acid sequences disclosed herein are contemplated and encompassed by this disclosure. A representative BLASTP setting that uses an Expect Threshold of 10, a Word Size of 3, BLOSUM 62 as a matrix, and Gap Penalty of 11 (Existence) and 1 (Extension) and a conditional compositional score matrix adjustment. Other default settings for BLASTP are described by and incorporated by reference to the disclosure available at: https://blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastp&PAGE_TYPE=BlastSearch&LINK _LOC=blasthome (last accessed Jan. 27, 2017).
Yeast Expression.
In one embodiment, collagen molecules are produced in a yeast expression system. In yeast, a number of vectors containing constitutive or inducible promoters known in the art may be used; Ausubel et al., supra, Vol. 2, Chapter 13; Grant et al. (1987) Expression and Secretion Vectors for Yeast, in Methods in Enzymology, Ed. Wu & Grossman, Acad. Press, N.Y. 153:516-544; Glover (1986) DNA Cloning, Vol. II, IRL Press, Wash., D.C., Ch. 3; Bitter (1987) Heterologous Gene Expression in Yeast, in Methods in Enzymology, Eds. Berger & Kimmel, Acad. Press, N.Y. 152:673-684; and The Molecular Biology of the Yeast Saccharomyces, Eds. Strathern et al., Cold Spring Harbor Press, Vols. I and II (1982).
Collagen can be expressed using host cells, for example, from the yeast Saccharomyces cerevisiae. This particular yeast can be used with any of a large number of expression vectors. Commonly employed expression vectors are shuttle vectors containing the 2P origin of replication for propagation in yeast and the Col E1 origin for E. coli, for efficient transcription of the foreign gene. A typical example of such vectors based on 2P plasmids is pWYG4, which has the 2P ORI-STB elements, the GAL1-10 promoter, and the 2P D gene terminator. In this vector, an Ncol cloning site is used to insert the gene for the polypeptide to be expressed, and to provide the ATG start codon. Another expression vector is pWYG7L, which has intact 2αORI, STB, REP1 and REP2, and the GAL1-10 promoter, and uses the FLP terminator. In this vector, the encoding polynucleotide is inserted in the polylinker with its 5′ ends at a BamHI or Ncol site. The vector containing the inserted polynucleotide is transformed into S. cerevisiae either after removal of the cell wall to produce spheroplasts that take up DNA on treatment with calcium and polyethylene glycol or by treatment of intact cells with lithium ions.
Alternatively, DNA can be introduced by electroporation. Transformants can be selected, for example, using host yeast cells that are auxotrophic for leucine, tryptophan, uracil, or histidine together with selectable marker genes such as LEU2, TRP1, URA3, HIS3, or LEU2-D.
In one embodiment, polynucleotides encoding collagen are introduced into host cells from the yeast Pichia. Species of non-Saccharomyces yeast such as Pichia pastoris appear to have special advantages in producing high yields of recombinant protein in scaled up procedures. Additionally, a Pichia expression kit is available from Invitrogen Corporation (San Diego, Calif.).
There are a number of methanol responsive genes in methylotrophic yeasts such as Pichia pastoris, the expression of each being controlled by methanol responsive regulatory regions, also referred to as promoters. Any of such methanol responsive promoters are suitable for use in the practice of the present invention. Examples of specific regulatory regions include the AOX1 promoter, the AOX2 promoter, the dihydroxyacetone synthase (DAS), the P40 promoter, and the promoter for the catalase gene from P. pastoris, etc.
In other embodiments, the methylotrophic yeast Hansenula polymorpha is used. Growth on methanol results in the induction of key enzymes of the methanol metabolism, such as MOX (methanol oxidase), DAS (dihydroxyacetone synthase), and FMHD (formate dehydrogenase). These enzymes can constitute up to 30-40% of the total cell protein. The genes encoding MOX, DAS, and FMDH production are controlled by strong promoters induced by growth on methanol and repressed by growth on glucose. Any or all three of these promoters may be used to obtain high-level expression of heterologous genes in H. polymorpha. Therefore, in one aspect, a polynucleotide encoding animal collagen or fragments or variants thereof is cloned into an expression vector under the control of an inducible H. polymorpha promoter. If secretion of the product is desired, a polynucleotide encoding a signal sequence for secretion in yeast is fused in frame with the polynucleotide. In a further embodiment, the expression vector preferably contains an auxotrophic marker gene, such as URA3 or LEU2, which may be used to complement the deficiency of an auxotrophic host.
The expression vector is then used to transform H. polymorpha host cells using techniques known to those of skill in the art. A useful feature of H. polymorpha transformation is the spontaneous integration of up to 100 copies of the expression vector into the genome. In most cases, the integrated polynucleotide forms multimers exhibiting a head-to-tail arrangement. The integrated foreign polynucleotide has been shown to be mitotically stable in several recombinant strains, even under non-selective conditions. This phenomena of high copy integration further ads to the high productivity potential of the system.
Fungal Expression.
Filamentous fungi may also be used to produce the present polypeptides. Vectors for expressing and/or secreting recombinant proteins in filamentous fungi are well known, and one of skill in the art could use these vectors to express the recombinant animal collagens of the present invention.
Plant Expression.
In one aspect, an animal collagen is produced in a plant or plant cells. In cases where plant expression vectors are used, the expression of sequences encoding the collagens of the invention may be driven by any of a number of promoters. For example, viral promoters such as the 35S RNA and 19S RNA promoters of CaMV (Brisson et al. (1984) Nature 310:511-514), or the coat protein promoter of TMV (Takamatsu et al. (1987) EMBO J. 6:307-311) may be used; alternatively, plant promoters such as the small subunit of RUBISCO (Coruzzi et al. (1984) EMBO J. 3:1671-1680; Broglie et al. (1984) Science 224:838-843) or heat shock promoters, e.g., soybean hsp17.5-E or hsp17.3-B (Gurley et al. (1986) Mol. Cell. Biol. 6:559-565) may be used. These constructs can be introduced into plant cells by a variety of methods known to those of skill in the art, such as by using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transformation, microinjection, electroporation, etc. For reviews of such techniques see, for example, Weissbach & Weissbach, Methods for Plant Molecular Biology, Academic Press, NY, Section VIII, pp. 421-463 (1988); Grierson & Corey, Plant Molecular Biology, 2d Ed., Blackie, London, Ch. 7-9 (1988); Transgenic Plants: A Production System for Industrial and Pharmaceutical Proteins, Owen and Pen eds., John Wiley & Sons, 1996; Transgenic Plants, Galun and Breiman eds, Imperial College Press, 1997; and Applied Plant Biotechnology, Chopra, Malik, and Bhat eds., Science Publishers, Inc., 1999.
Plant cells do not naturally produce sufficient amounts of post-translational enzymes to efficiently produce stable collagen. Therefore, where hydroxylation is desired, plant cells used to express animal collagens are supplemented with the necessary post-translational enzymes to sufficiently produce stable collagen. In a preferred embodiment of the present invention, the post-translational enzyme is prolyl 4-hydroxylase.
Methods of producing the present animal collagens in plant systems may be achieved by providing a biomass from plants or plant cells, wherein the plants or plant cells comprise at least one coding sequence is operably linked to a promoter to effect the expression of the polypeptide, and the polypeptide is then extracted from the biomass. Alternatively, the polypeptide can be non-extracted, e.g., expressed into the endosperm.
Plant expression vectors and reporter genes are generally known in the art; See, e.g., Gruber et al. (1993) in Methods of Plant Molecular Biology and Biotechnology, CRC Press. Typically, the expression vector comprises a nucleic acid construct generated, for example, recombinantly or synthetically, and comprising a promoter that functions in a plant cell, wherein such promoter is operably linked to a nucleic acid sequence encoding an animal collagen or fragments or variants thereof, or a post-translational enzyme important to the biosynthesis of collagen.
Promoters drive the level of protein expression in plants. To produce a desired level of protein expression in plants, expression may be under the direction of a plant promoter. Promoters suitable for use in accordance with the present invention are generally available in the art; See, e.g., PCT Publication No. WO 91/19806. Examples of promoters that may be used in accordance with the present invention include non-constitutive promoters or constitutive promoters. These promoters include, but are not limited to, the promoter for the small subunit of ribulose-1,5-bis-phosphate carboxylase; promoters from tumor-inducing plasmids of Agrobacterium tumefaciens, such as the RUBISCO nopaline synthase (NOS) and octopine synthase promoters; bacterial T-DNA promoters such as mas and ocs promoters; and viral promoters such as the cauliflower mosaic virus (CaMV) 19S and 35S promoters or the figwort mosaic virus 35S promoter.
The polynucleotide sequences of the present invention can be placed under the transcriptional control of a constitutive promoter, directing expression of the collagen or post-translational enzyme in most tissues of a plant. In one embodiment, the polynucleotide sequence is under the control of the cauliflower mosaic virus (CaMV) 35S promoter. The double stranded caulimorvirus family has provided the single most important promoter expression for transgene expression in plants, in particular, the 35S promoter; See, e.g., Kay et al. (1987) Science 236:1299. Additional promoters from this family such as the figwort mosaic virus promoter, etc., have been described in the art, and may also be used; See, e.g., Sanger et al. (1990) Plant Mol. Biol. 14:433-443; Medberry et al. (1992) Plant Cell 4:195-192; and Yin and Beachy (1995) Plant J. 7:969-980.
The promoters used in polynucleotide constructs for expressing collagen may be modified, if desired, to affect their control characteristics. For example, the CaMV promoter may be ligated to the portion of the RUBISCO gene that represses the expression of RUBISCO in the absence of light, to create a promoter which is active in leaves, but not in roots. The resulting chimeric promoter may be used as described herein.
Constitutive plant promoters having general expression properties known in the art may be used with the expression vectors of the present invention. These promoters are abundantly expressed in most plant tissues and include, for example, the actin promoter and the ubiquitin promoter; See, e.g., McElroy et al. (1990) Plant Cell 2:163-171; and Christensen et al. (1992) Plant Mol. Biol. 18:675-689.
Alternatively, the polypeptide of the present invention may be expressed in a specific tissue, cell type, or under more precise environmental conditions or developmental control. Promoters directing expression in these instances are known as inducible promoters. In the case where a tissue-specific promoter is used, protein expression is particularly high in the tissue from which extraction of the protein is desired. Depending on the desired tissue, expression may be targeted to the endosperm, aleurone layer, embryo (or its parts as scutellum and cotyledons), pericarp, stem, leaves tubers, roots, etc. Examples of known tissue-specific promoters include the tuber-directed class I patatin promoter, the promoters associated with potato tuber ADPGPP genes, the soybean promoter of β-conglycinin (7S protein) which drives seed-directed transcription, and seed-directed promoters from the zein genes of maize endosperm; See, e.g., Bevan et al. (1986) Nucleic Acids Res. 14: 4625-38; Muller et al. (1990) Mol. Gen. Genet. 224:136-46; Bray (1987) Planta 172: 364-370; and Pedersen et al. (1982) Cell 29:1015-26.
Collagen polypeptides can be produced in seed by way of seed-based production techniques using, for example, canola, corn, soybeans, rice and barley seed. In such a process, for example, the product is recovered during seed germination; See, e.g., PCT Publication Numbers WO 9940210; WO 9916890; WO 9907206; U.S. Pat. Nos. 5,866,121; 5,792,933; and all references cited therein. Promoters that may be used to direct the expression of the polypeptides may be heterologous or non-heterologous. These promoters can also be used to drive expression of antisense nucleic acids to reduce, increase, or alter concentration and composition of the present animal collagens in a desired tissue.
Other modifications that may be made to increase and/or maximize transcription of the present polypeptides in a plant or plant cell are standard and known to those in the art. For example a vector comprising a polynucleotide sequence encoding a recombinant animal collagen, or a fragment or variant thereof, operably linked to a promoter may further comprise at least one factor that modifies the transcription rate of collagen or related post-translational enzymes, including, but not limited to, peptide export signal sequence, codon usage, introns, polyadenylation, and transcription termination sites. Methods of modifying constructs to increase expression levels in plants are generally known in the art; See, e.g. Rogers et al. (1985) J. Biol. Chem. 260:3731; and Cornejo et al. (1993) Plant Mol Biol 23:567-58. In engineering a plant system that affects the rate of transcription of the present collagens and related post-translational enzymes, various factors known in the art, including regulatory sequences such as positively or negatively acting sequences, enhancers and silencers, as well as chromatin structure can affect the rate of transcription in plants. at least one of these factors may be utilized when expressing a recombinant animal collagen, including but not limited to the collagen types described above.
The vectors comprising the present polynucleotides will typically comprise a marker gene which confers a selectable phenotype on plant cells. Usually, the selectable marker gene will encode antibiotic resistance, with suitable genes including at least one set of genes coding for resistance to the antibiotic spectinomycin, the streptomycin phophotransferase (SPT) gene coding for streptomycin resistance, the neomycin phophotransferase (NPTH) gene encoding kanamycin or geneticin resistance, the hygromycin resistance, genes coding for resistance to herbicides which act to inhibit the action of acetolactate synthase (ALS), in particular, the sulfonylurea-type herbicides; e.g., the acetolactate synthase (ALS) gene containing mutations leading to such resistance in particular the S4 and/or Hra mutations, genes coding for resistance to herbicides which act to inhibit action of glutamine synthase, such as phophinothricin or basta; e.g. the bar gene, or other similar genes known in the art. The bar gene encodes resistance to the herbicide basta, the nptll gene encodes resistance to the antibiotics kanamycin and geneticin, and the ALS gene encodes resistance to the herbicide chlorsulfuron.
Typical vectors useful for expression of foreign genes in plants are well known in the art, including, but not limited to, vectors derived from the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens. These vectors are plant integrating vectors that upon transformation, integrate a portion of the DNA into the genome of the host plant; see e.g., Rogers et al. (1987) Meth In Enzymol. 153:253-277; Schardl et al. (1987) Gene 61:1-11; and Berger et al., Proc. Natl. Acad. Sci. U.S.A. 86:8402-8406.
Vectors comprising sequences encoding the present polypeptides and vectors comprising post-translational enzymes or subunits thereof may be co-introduced into the desired plant. Procedures for transforming plant cells are available in the art, for example, direct gene transfer, in vitro protoplast transformation, plant virus-mediated transformation, liposome-mediated transformation, microinjection, electroporation, Agrobacterium mediated transformation, and particle bombardment; see e.g., Paszkowski et al. (1984) EMBO J. 3:2717-2722; U.S. Pat. No. 4,684,611; European Application No. 0 67 553; U.S. Pat. Nos. 4,407,956; 4,536,475; Crossway et al. (1986) Biotechniques 4:320-334; Riggs et al. (1986) Proc. Natl. Acad. Sci USA 83:5602-5606; Hinchee et al. (1988) Biotechnology 6:915-921; and U.S. Pat. No. 4,945,050.) Standard methods for the transformation of, e.g., rice, wheat, corn, sorghum, and barley are described in the art; See, e.g., Christou et al. (1992) Trends in Biotechnology 10: 239 and Lee et al. (1991) Proc. Nat'l Acad. Sci. USA 88:6389. Wheat can be transformed by techniques similar to those employed for transforming corn or rice. Furthermore, Casas et al. (1993) Proc. Nat'l Acad. Sci. USA 90:11212, describe a method for transforming sorghum, while Wan et al. (1994) Plant Physiol. 104: 37, teach a method for transforming barley. Suitable methods for corn transformation are provided by Fromm et al. (1990) Bio/Technology 8:833 and by Gordon-Kamm et al., supra.
Additional methods that may be used to generate plants that produce animal collagens of the present invention are established in the art; See, e.g., U.S. Pat. Nos. 5,959,091; 5,859,347; 5,763,241; 5,659,122; 5,593,874; 5,495,071; 5,424,412; 5,362,865; 5,229,112; 5,981,841; 5,959,179; 5,932,439; 5,869,720; 5,804,425; 5,763,245; 5,716,837; 5,689,052; 5,633,435; 5,631,152; 5,627,061; 5,602,321; 5,589,612; 5,510,253; 5,503,999; 5,378,619; 5,349,124; 5,304,730; 5,185,253; 4,970,168; European Publication No. EPA 00709462; European Publication No. EPA 00578627; European Publication No. EPA 00531273; European Publication No. EPA 00426641; PCT Publication No. WO 99/31248; PCT Publication No. WO 98/58069; PCT Publication No. WO 98/45457; PCT Publication No. WO 98/31812; PCT Publication No. WO 98/08962; PCT Publication No. WO 97/48814; PCT Publication No. WO 97/30582; and PCT Publication No. WO 9717459.
Insect Expression.
Another alternative expression system for collagen is an insect system. Baculoviruses are very efficient expression vectors for the large scale production of various recombinant proteins in insect cells. The methods as described in Luckow et al. (1989) Virology 170:31-39 and Gruenwald, S. and Heitz, J. (1993) Baculovirus Expression Vector System: Procedures & Methods Manual, Pharmingen, San Diego, Calif., can be employed to construct expression vectors containing a collagen coding sequence for the collagens of the invention and the appropriate transcriptional/translational control signals. For example, recombinant production of proteins can be achieved in insect cells, by infection of baculovirus vectors encoding the polypeptide. The production of recombinant collagen, collagen-like or collagenous polypeptides with stable triple helices can involve the co-infection of insect cells with three baculoviruses, one encoding the animal collagen to be expressed and one each encoding the α subunit and β subunit of prolyl 4-hydroxylase. This insect cell system allows for production of recombinant proteins in large quantities. In one such system, Autographa californica nuclear polyhidrosis virus (AcNPV) is used as a vector to express foreign genes. This virus grows in Spodoptera frugiperda cells. Coding sequences for collagen or collagen-like polypeptides may be cloned into non-essential regions (for example the polyhedron gene) of the virus and placed under control of an AcNPV promoter (for example, the polyhedron promoter). Successful insertion of a coding sequence will result in inactivation of the polyhedron gene and production of non-occluded recombinant virus; e.g., viruses lacking the proteinaceous coat coded for by the polyhedron gene. These recombinant viruses are then used to infect Spodoptera frugiperda cells in which the inserted gene is expressed; see, e.g., Smith et al. (1983) J. Virol. 46:584; and U.S. Pat. No. 4,215,051. Further examples of this expression system may be found in, for example, Ausubel et al. above.
Animal Expression.
In animal host cells, a number of expression systems may be utilized. In cases where an adenovirus is used as an expression vector, polynucleotide sequences encoding collagen or collagen-like polypeptides may be ligated to an adenovirus transcription/translation control complex, e.g., the late promoter and tripartite leader sequence. This chimeric gene may then be inserted in the adenovirus genome by in vitro or in vivo recombination. Insertion in a non-essential region of the viral genome (e.g., region E1 or E3) will result in a recombinant virus that is viable and capable of expressing the encoded polypeptides in infected hosts; see, e.g., Logan & Shenk, Proc. Natl. Acad. Sci. USA 81:3655-3659 (1984). Alternatively, the vaccinia 7.5 K promoter may be used; see, e.g., Mackett et al. (1982) Proc. Natl. Acad. Sci. USA 79:7415-7419; Mackett et al. (1982) J. Virol. 49:857-864; and Panicali et al. (1982) Proc. Natl. Acad. Sci. USA 79:4927-4931.
A preferred expression system in mammalian host cells is the Semliki Forest virus. Infection of mammalian host cells, for example, baby hamster kidney (BHK) cells and Chinese hamster ovary (CHO) cells can yield very high recombinant expression levels. Semliki Forest virus is a preferred expression system as the virus has a broad host range such that infection of mammalian cell lines will be possible. More specifically, Semliki Forest virus can be used in a wide range of hosts, as the system is not based on chromosomal integration, and thus provides an easier way of obtaining modifications of the recombinant animal collagens in studies aiming at identifying structure function relationships and testing the effects of various hybrid molecules. Methods for constructing Semliki Forest virus vectors for expression of exogenous proteins in mammalian host cells are described in, for example, Olkkonen et al. (1994) Methods Cell Biol 43:43-53.
Non-human Transgenic animals may also be used to express the polypeptides of the present invention. Such systems can be constructed by operably linking the polynucleotide of the invention to a promoter, along with other required or optional regulatory sequences capable of effecting expression in mammary glands. Likewise, required or optional post-translational enzymes may be produced simultaneously in the target cells employing suitable expression systems. Methods of using non-human transgenic animals to recombinantly produce proteins are known in the art; See, e.g., U.S. Pat. Nos. 4,736,866; 5,824,838; 5,487,992; and U.S. Pat. No. 5,614,396.
The references cited in the sections above which describe the production of recombinant collagens are each incorporated by reference.
Composite Collagen Fiber Sheets.
As shown in FIG. 1, triple helical collagen molecules associate into fibrils which in animal skin assemble into larger fibril bundles or collagen fibers. Prior methods of making collagen sheets used a mixture of ground animal skin or leather scraps and dissolved or suspended collagen. Such collagen fiber-containing products are described by U.S. Pat. Nos. 2,934,446; 3,073,714; 3,122, 599; and 3,136,682. Highberger, et al., U.S. Pat. No. 2,934,446 describes a method using a meat grinder to produce a slurry of calfskin hide or corium which is formed into a sheet, tanned and for forming interlocked collagen fiber masses by comminuting and dispersing animal skin in an acidic aqueous solution at 5° C. and then raising the pH and temperature to precipitate collagen fibers to form a gel which is then dried. These sheets of collagen fiber masses make use of leather scraps and form sheets resembling leather. Highberger does not show that these leather sheets are suitable for commercial use. Tu, et al., U.S. Pat. No. 3,073,714 discloses producing a sheet from an calfskin slurry containing 25% solids which is tanned with a vegetable tanning solution and treated with glycerin and oleic acid. These collagen fiber sheets are described as reproducing the internal arrangement of collagen fibers in natural skins and hides. Tu does not show that the leather sheets are compositionally or aesthetically suitable for use in a consumer product. Tu, et al., U.S. Pat. No. 3,122,599 describes a leather-like sheet made from ground animal skin or leather which contains collagen fibers and soluble collagen as well as other components derived from the animal skin. Tu discloses treating this mixture with chromium, dehydrating it with acetone, and treating with oleic acid to produce a leather-like product containing collagen fiber masses. Tu does not show that the sheet is compositionally, physically or aesthetically suitable for use in a consumer product. Tu, et al., U.S. Pat. No. 3,136,682 describes a process of making a leather-like material that contains a mixture of collagen fibers and a binder of water-soluble proteinaceous material derived from animal skin. It also describes the use of a chromium tanning agent and treatment with oleic acid. Tu describes a sheet of good appearance and feel, but does not show that it is suitable for incorporation into a consumer product. These products incorporate coarse, ground or digested collagen fibers.
Cultured Leather Products.
These products generally comprise a plurality of layers containing collagen produced by culturing cells in vitro are described by Forgacs, et al., U.S. 2016/0097109 A1 and by Greene, U.S. Pat. No. 9,428,817 B2. These products are produced in vitro by cultivation of cell explants or cultured collagen-producing cells. Such cells produce and process collagen into quaternary bundles of collagen fibrils and do not have the random, non-antistrophic structure of the collagen fibrils of the invention. Forgacs describes engineered animal skins, which may be shaped, to produce a leather product. Green describes a variety of products, such as footwear, apparel and luggage that may incorporate leather that is cultured in vitro. US 2013/0255003 describes producing collagen for leather-like products by growing bovine skin cells in culture. Other types of host cells have been utilized to produce collagen for medical implants or to produce gelatin. For example, United States Patent Application US 2004/0018592 describes a way to produce gelatin by recombinantly expressing bovine collagen in host cells, such as yeast.
Medical Products.
Networks of collagen have been produced in vitro as materials for biomedical applications. In those applications, monomers of the collagen triple helix are extracted from animal tissue, such as bovine dermis, either by acid treatment or treatment with protein degrading enzymes such as pepsin, to solubilize collagen from the tissue. Once purified, these solubilized collagens (often mixtures of monomers, dimers and trimers of the collagen triple helix) can be fibrillated into fibrils through a pH shift in aqueous buffers. Under the right conditions, the collagen monomers self-assemble into fibrils, and depending on their source and how they were isolated, the fibrils can physically crosslink to form a solid hydrogel. In addition, recombinant collagens and collagen-like proteins have been shown to fibrillate in vitro through similar adjustments in pH and salt concentration. Examples of such products for medical applications include a biodegradable collagen matrix made from a collagen slurry that self-assembles into macroscopic collagen fibers, U.S. Pat. No. 9,539,363, and an organized array of collagen fibrils produced by use of external guidance structures or internal templates and the application of tension, U.S. Pat. No. 9,518,106. Collagen products used in medicine, such as for tissue engineering or grafting, often aim to provide collagen in a form similar to that in a particular tissue being engineered or repaired. While fibrillation of soluble collagens and collagen-like proteins has been explored to produce collagen hydrogels for biomedical applications, this technology has not been successfully applied to the production of a material having the strength and aesthetic properties of natural leather.
Synthetic Plastic-Based Leathers.
Attempts to create synthetic leather have come up short in reproducing leather's unique set of functional and aesthetic properties. Examples of synthetic leather materials include Clarino, Naugahyde®, Corfam, and Alcantara, amongst others. They are made of various chemical and polymer ingredients, including polyvinyl chloride, polyurethane, nitrocellulose coated cotton cloth, polyester, or other natural cloth or fiber materials coated with a synthetic polymer. These materials are assembled using a variety of techniques, often drawing from chemical and textile production approaches, including nonwoven and advanced spinning processes. While many of these materials have found use in footwear, upholstery, and apparel applications, they have fallen short for luxury application, as they cannot match the breathability, performance, hand feel, or aesthetic properties that make leather so unique and beloved. To date, no alternative commercial leather-like materials have been made from a uniform network of collagen or collagen-like proteins. Synthetic plastic materials lack the chemical composition and structure of a collagen network that produces an acceptable leather aesthetic. Unlike, synthetics, the chemical composition of amino acid side groups along the collagen polypeptide chain, along with its organization into a strong yet porous, fibrous architecture allow stabilization and functionalization of the fibril network through crosslinking processes to produce the desirable strength, softness and aesthetic of leather.
While fibrillation of soluble collagens and collagen-like proteins has been explored to bind together ground or comminuted leather scraps or for the production of collagen hydrogels for biomedical applications, harnessing this phenomenon to produce a commercially acceptable leather-like material has not been achieved.
In view of the problems with prior art natural leathers, and composite, cultured, and synthetic, plastic-based leather products the inventors diligently pursued a way to provide a biofabricated leather having superior strength and uniformity and non-anisotropic properties that incorporated natural components found in leather.
Described herein are materials composed of collagen fibrils fibrillated in vitro that have leather-like properties imparted by crosslinking, dehydration and lubrication. Compared to tanned and fatliquored animal hides, these biofabricated materials can have structural, compositional and functional uniformity, for example, advantageous substantially non-anisotropic strength and other mechanical properties as well as a top grain like aesthetic on both their top and bottom surfaces.